bzoj 3365 [Usaco2004 Feb]Distance Statistics 路程统计（点分治，单调）

  1 #include<set>
  2 #include<cmath>
  3 #include<queue>
  4 #include<vector>
  5 #include<cstdio>
  6 #include<cstring>
  7 #include<iostream>
  8 #include<algorithm>
  9 #define trav(u,i) for(int i=front[u];i;i=e[i].nxt)
 10 #define FOR(a,b,c) for(int a=(b);a<=(c);a++)
 11 using namespace std;
 12 
 13 typedef long long ll;
 14 const int N = 2e5+10; 
 15 
 16 ll read() {
 17     char c=getchar();
 18     ll f=1,x=0;
 19     while(!isdigit(c)) {
 20         if(c==‘-‘) f=-1; c=getchar();
 21     }
 22     while(isdigit(c))
 23         x=x*10+c-‘0‘,c=getchar();
 24     return x*f;
 25 }
 26 
 27 struct Edge {
 28     int v,w,nxt;
 29 }e[N<<1];
 30 int en=1,front[N];
 31 void adde(int u,int v,int w) 
 32 {
 33     e[++en]=(Edge){v,w,front[u]}; front[u]=en;
 34 }
 35 
 36 int n,m,K,ans;
 37 int rt,size,list[N],vis[N],dis[N],siz[N],f[N],l1,l2;
 38 
 39 bool cmp(const int& x,const int& y)
 40 {
 41     return dis[x]<dis[y];
 42 }
 43 void get_root(int u,int fa) 
 44 {
 45     siz[u]=1; f[u]=0;
 46     trav(u,i) if(!vis[e[i].v]&&e[i].v!=fa){
 47         int v=e[i].v;
 48         get_root(v,u);
 49         siz[u]+=siz[v];
 50         if(f[u]<siz[v]) f[u]=siz[v];
 51     }
 52     f[u]=max(f[u],size-siz[u]);
 53     if(f[u]<f[rt]) rt=u;
 54 }
 55 void dfs(int u,int fa) 
 56 {
 57     list[++l1]=u;
 58     trav(u,i) 
 59     if(!vis[e[i].v]&&e[i].v!=fa) {
 60         int v=e[i].v;
 61         dis[v]=dis[u]+e[i].w;
 62         dfs(v,u);
 63     }
 64 }
 65 int get_ans(int l,int r) 
 66 {
 67     sort(list+l,list+r+1,cmp);
 68     int j=r,ans=0;
 69     for(int i=l;i<=r;i++) {
 70         while(j>i&&dis[list[j]]+dis[list[i]]>K) j--;
 71         ans+=j-i; if(i==j) break; 
 72     }
 73     return ans;
 74 }
 75 void solve(int u)
 76 {
 77     vis[u]=1; l1=l2=0;
 78     trav(u,i) if(!vis[e[i].v]) {
 79         int v=e[i].v;
 80         dis[v]=e[i].w;
 81         dfs(v,-1);
 82         ans-=get_ans(l2+1,l1);
 83         l2=l1;
 84     }
 85     list[++l1]=u; dis[u]=0;
 86     ans+=get_ans(1,l1);
 87     trav(u,i) if(!vis[e[i].v]) {
 88         rt=0; get_root(e[i].v,-1);
 89         size=siz[e[i].v];
 90         solve(rt);
 91     }
 92 }
 93 
 94 int main()
 95 {
 96     n=read(),m=read();
 97     int u,v,w; char s[5];
 98     FOR(i,1,m) {
 99         u=read(),v=read(),w=read();
100         adde(u,v,w),adde(v,u,w);
101         scanf("%s",s);
102     }
103     K=read();
104     size=f[0]=n;
105     get_root(1,-1);
106     solve(rt);
107     printf("%d\n",ans);
108     return 0;
109 }